In recent years, in stores and the like in the apparel industry, a system for attaching radio tags such as RFID (Radio Frequency Identification) tags to commodities and performing information collection and analyses such as receiving and shipping of commodities, inventory, and stock management is used.
As an example of this kind of the system, there is known a system for realizing, using a technique concerning RFID, a commodity shelf (also referred to as smart shelf) capable of acquiring information concerning commodities picked up by customers and a stock of the commodities on a real time basis. This system is configured to radiate a radio wave from an antenna set in a lower part of the commodity shelf to read, as required, radio tags affixed to commodities placed on the commodity shelf and, if there is a radio tag that cannot be read, discriminate that a commodity affixed with the radio tag is picked up by a customer and removed from the commodity shelf.
In order to improve discrimination accuracy in the commodity shelf, it is necessary to prevent the radio wave radiated from the antenna from leaking to the outside of the commodity shelf and enable radio tags in the commodity shelf to be surely read. In order to prevent the radio wave radiated from the antenna from leaking to the outside of the commodity shelf, it is necessary to sharpen the radiation pattern of the antenna. However, if the radiation pattern is sharp, a dead zone where the radio tags cannot be read is formed in the commodity shelf. It is conceivable to cope with such a problem using, for example, a method of reading the radio tags while switching plural antennas or a method of controlling phases of signals to array antenna elements using an array antenna to control a radiation direction of the antenna.
However, in the method of switching the antennas, in a distance near from the antennas in which radio waves radiated from the antennas do not completely spread, a dead zone is formed near the middle of the antennas to be switched. It is possible to solve this problem by densely laying the antennas. However, because of a space occupied by the antennas themselves, the antennas cannot be sufficiently densely laid. In the method of controlling the radiation direction of the antenna, a radio wave leaks to the outside of the commodity shelf.
Under such circumstances, it is necessary to take measures for enabling sure reading of radio tags present in a specific area while limiting a communication area of an antenna within the specific area.